Leathernecks often say if it's not raining, they're not training. The next time thousands of them deploy to Australia's Northern Territory, that could very much be true.

The Marine Corps announced this week that it would delay an annual rotation Down Under due to the novel coronavirus pandemic. Thousands of California- and Hawaii-based Marines -- along with MV-22 Ospreys, AH-1Z Vipers, UH-1Y Venoms and RQ-21 Blackjacks -- were scheduled to deploy to Darwin this spring.

The rotation, which now sends about 2,500 Marines to the country annually, is considered vital to the service's mission in the Pacific. It typically occurs only during the dry season though, since heavy rainfall can flood training areas between November and April.

Now, the Marine air-ground task force that deploys there could do so during that period.

"The Marine Corps remains prepared to conduct the deployment later this year if the situation permits, keeping within health and force protection concerns," said Chuck Little, a Marine Corps Forces Pacific spokesman. "Any announcement regarding possible resumption of the deployment would come from the government of Australia, in coordination with the U.S. government."

The Northern Territory's wet season runs from November to April, and can bring high humidity, monsoon rains and tropical storms, according to the area's tourism site. Temperatures can peak in the 90s during the day, and humidity reaches more than 80%.

"With heavy rains, some roads can become flooded at this time of year, and there can be a risk of cyclones,"the site states. But the season also brings "thundering waterfalls" and "magnificent escarpments with lush foliage clean after the rains," it adds.

The Marine Corps has been sending units to Australia for nearly a decade, building up to a full 2,500-person rotation last year. Marines there not only train with Aussie forces, but other partners from the Asia-Pacific region.

Officials were initially planning to have the 2,500 Marines stay in their barracks for 14 days upon arriving in Australia to prevent any coronavirus spread. Weeks later, the rotation was delayed indefinitely.

The Marine Corps is still sending vehicles and other supplies to Australia in anticipation of the rotation happening this year, Little said. Australian authorities have strict quarantine and inspection requirements.

In the meantime, the units and squadrons that were supposed to deploy will continue training to retain their mission capabilities, Little said. The units, he added, will be announced once U.S. and Australian officials agree on a new start date for the rotation.